Radioreceiver



Feb. 11, 1930. H. J. ROUND ET AL RADIOR-ECEIVER Filed April 6. 1925 INVENTOR HENRY J ROUND AND I B NOEL EYER RUST ATTORNEY Patented Feb. 11, 1930 UNITED STATES PATENT oFFIc HENRY JOSEPH ROUND, OF LONDON, AND NOEL MEYER RUST, 0F CHEL'MSFORD, ENGLAND, ASSIGNORS TO RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE RADIORECEIVEB Application filed April 6, 1925, Serial No. 20,902, and in Great Britain April 9, 1924.

This invention relates to means for obtaining negative resistance effects, and to improvements in radio receivers.

In applying the invention to diminishing the resistance of an aerial (in other words to obtain negative resistance), we connect or couple to the aerial inductance a circuit con taining a crystal and a condenser in series with one another, the crystal being shunted with a high resistance and. a battery in series with one another. To the aerial inductance we also connect or couple a circuit containing a rectifier (preferably another crystal) in series with a telephone or pair of telephones which is shunted by a condenser and with a potentiometer.

In order to give some idea of the constants of these circuits we may say that we have found the following to besuitable for use in the reception of broadcasted news with an aerial consisting of an ordinary single wire of length about 80 feet and height about 20 feet, connected through a .003 mitd. condenser and an ordinary broadcast ,variometer to earth. To the high potential end of the varicluster was connected one side of a variable condenser having amaximum value of about .0008 mtd; during working the value of this condenser was between .0001 and .00025. The other side of this condenser was connected to a crystal the cats whisker contact of which was connected to the earthed end of the variometer. The crystal was also connected to one end of a resistance which could be varied between 1000 and 12000 ohms, and the other end of this resistance was connected to the positive pole of a volt battery which could be tapped with variations of 1 volts, the negative pole being connected to the cats whisker. The best results were obtained with the highest values of the resistance and of the battery voltage practicable, but not more than 50 volts are advisable as with higher voltages the cats whisker is apt to get burnt when adjusting. To the high potential end of the variometer was also connected a carborundum crystal, and its metallic contact was connected to a pair of ordinary high resistance telephones shunted by a 10 jar disc 1 condenser generally used at low value, and

this again to the usual potentiometer and then to the lower end of the variometer.

When receiving wave lengths of the order of 350 meters the aerial inductance may be of the order of 150 microhenries. For 3500 meters the value of the aerial condenser would depend on the aerial employed while for small aerials such a condenser would not be necessary except for fine tuning. The value of the condenser in series with the negative resistance crystal would be of the order of @002 mid. and that of the aerial inductance from 1000 to 1500 microhenries, while for greater wave lengths the values of this condenser I and of the inductance should be roughly proportional to the wave length.

lVe have found that to obtain the negative resistance eifect, the best results are obtained with crystals of low resistance, thus arzenite, silicon, zincite, tellurium, magnetite and iron pyrites, may be employed, these names being arranged in the order of the efficiency of the crystals.

Arzenite is the trade name of a new product and is a nearly pure crystalline form of zinc oxide.

The characteristic curve of each of these crystals possesses a sharply defined kink or knee and to obtain the negative resistance effect the value of the resistance in series with the crystal should be so great that the part above the knee of the characteristic of the' crystal and resistance combined is. not too steep, otherwise the circuit will be unstable.

We have found, however, that by using a smaller resistance so that the combination of the crystal and resistance has a negative characteristic, oscillations will be set up in the crystal circuit and then, super regenerative efiiects can be obtained,v owing to the automatic quenching eftects of the rectifier crystal.

We have found also that the negative resistance effect to be obtained from crystals of arzenite, zincite, tellurium and magnetite (especially the first two) is increased if the. operative surface of the crystal is fused. The method of fusing is, preferably, to secure the crystal in a cup with zinc, care being taken to pushthe crystal well into the; molten. Zinc before it sets, so as to ensure that the crystal is well gripped by the metal as it cools. The crystal is then gripped in a vise which is connected through a 7 .5 ohm resistance to the positive pole of a 100 volt source of direct current. A carbon electrode is connected to the negative pole and an arc is struck between the carbon and the face of the crystal. The carbon is moved backwards and forwards several times so that the arc is drawn out and contracted. A slight crater of darkly glazed material is thus formed on the crystal. The carbons for this process should be fairly small and kept sharply pointed.

\Ve may employ more than one crystal or crystal contact and preferably we employ a separate control resistance for each crystal.

lVe can thus afford to damp our aerial more by lower resistance rectifiers or by rectifiers in parallel, providing we have more negative resistance furnished by the crystals in parallel referred to above, to provide the necessary energy for obtaining the same potential across the rectifiers. In cases where better tuning is required, we find it advantageous to use a coupled circuit to our crystal and to apply a negative resistance crystal in a similar way to the secondary circuit or to both aerial and secondary circuit. It is well known that maximum transfer of energy at resonance willthentake place at a much looser coupling and the result of two low damped circuits coupled loosely will be very sharp over all resonance.

e may also employ a crystal connected in such a circuit for reducing the damping of a rejector circuit employed for eliminating one particular wave length.

In place of employing the crystals referred to above, we may employ a metal plate which has had a film of oxide produced on it by striking an arc on its surface. Suitable metals for use in this way are zinc, aluminium, iron, copper and nickel.

Ve apply to the film of oxide on such a plate a loose contact, such as a cats whisker, and connect this contact to a resistance and a source of current and so to the back of the plate. The contact and the back of the plate we also connect to an output circuit and are thus enabled to obtain in this output circuit a negative resistance effect or oscillations as desired.

In some cases we may even employ a plate on which a film of oxide has been produced naturally in the atmosphere or by other means, but such plates are not nearly so efficient as those in which the oxide has been produced by an arc. In fact we have not yetbeen able to produce stable oscillations from such plates, though we have obtained negative resistance effects from them, whereas with plates oxidized by an arc we have obtained oscillations of wave lengths of 8000 meters and over. We have found, however,

that by subjecting a zinc plate which has been coated with white oxide by an arc to a subsequent treatment with the arc a reddish brown oxide can be formed upon the white oxide and that oscillations as short as 600 meters can be obtained from points near the junction of this reddish brown oxide with the white oxide.

Preferably we so manipulate the are that this brown oxide is formed in a ring upon the white oxide.

The accompanying drawing illustrates various circuits in accordance with this invention. In the drawing Figure 1 illustrates diagrammatically an approved form of our invention and Figures 2, 3 and 4 illustrate modifications thereon.

In Fig. 1, the circuit A comprises a condenser 2, crystal or plate 8, as above described, a loose contact 4, such as a cats whisker which is applied to the crystal on plate 3, high resistance 5, and current source 6 connected to the aerial inductance 1, while the circuit B comprises rectifier 7 such as a carborundum crystal and telephones 8, also connected to the aerial inductance 1.

In the modification shown in Fig. 2, the circuit A is inductively coupled to the inductance 1, the circuit B being connected to the said inductance.

In Fig. 8 the circuit A is connected to the inductance 1 and the circuit B is inductively coupled thereto. In this case a condenser 9 is provided in circuit B. c

Fig. 4 illustrates a further modification,

in which three circuits A are employed, two

of the said circuits being connected to the inductance 1, and serving to produce negative resistance effects therein. The signals in the aerial are transferred to a secondary circuit and rectified as at B, negative resistance effects being introduced into this secondary circuit by the third circuit A.

Having described our invention, what we claim is:

1. Means for effectively reducing the resistance of an aerial circuit provided with an inductance, said means including an adjustable condenser and a rectifying crystal or oxidized plate in series therewith connected across said inductance, and a source of current and a resistance in series therewith connected in parallel with said rectifying crystal or oxidized plate.

2. Means for efiectively reducing the resistance of an aerial circuit provided with an inductance, said means including a circuit comprising an adjustable condenser and a rectifying crystal or oxidized plate in series therewith, and a source of current and a resistance in series therewith connected in parallel with said rectifying crystal or oxidized plate, said last mentioned circuit being inductivay coupled to the aerial inductance.

3. Means for reception, consisting of an aerial inductance, two circuits, one of which is connected to the inductance and contains a rectifying crystal and a condenser in series with one another, and a high resistance and a source of current connected across said crystal, the second circuit also being connected to the inductance and containing a rectifier in series with a sound responsive means.

at. Apparatus for receiving high frequency signals, including a detector circuit and an independent auxiliary circuit coupled thereto, said auxiliary circuit including a rectifying crystal means for obtaining a negative resistance effect and a biasing battery electrically associated with the crystal means.

5. Apparatus for receiving high frequency signals, including a detector circuit and an independent auxiliary circuit coupled there to, said auxiliary circuit including a rectifying oxidized plate shunted by a biasing battery for obtaining a negative resistance effeet.

6. Apparatus for receiving high frequency signals, including a detector circuit and an independent auxiliary circuit coupled thereto, said auxiliary circuit including a loW resistance rectifying crystal for obtainin a negative resistance effect, the operative ace of the crystal being fused and a source of potential connected to said crystal.

7. Apparatus for receiving high frequency signals, including an aerial, a circuit coupled to said aerial and comprising a rectifier and sound detecting means, and an independent auxiliary circuit also coupled to the aerial for efiectively reducing the resistance of the aerial, comprising a condenser and a low resistance rectifying crystal, and a source of current and a resistance in'series therewith connected across said crystal.

8. In a circuit, means for obtaining negative resistance whereby the circuit resistance may be effectively reduced, said means including a rectifying crystal of low resistance, the current-potential characteristic curve of which possesses a sharply defined knee.

9. Means for obtaining negative resistance, including a rectifying crystal or plate having a film of oxide formed upon its surface.

10. An arrangement for producing negative resistance effects comprising a rectifying crystal or oxidized plate shunted by a biasing battery, said crystal or oxidized plate having the characteristic of decreasing resistance with increase of potential beyond a certain critical value.

11. Means for obtaining negative resistance eifects comprising a tuned circuit having in series an inductance, a variable condenser and a low resistance rectifying crystal, and a biasing battery and resistance in parallel with said crystal, the arrangement being such that with increase of potential beyond a certain critical value the resistance ofthe crystal will decrease.

12. In a circuit, means, for reducing the resistance thereof, which comprises a second circuit coupled to said first circuit, said second circuit containing a rectifying crystal, and means, electrically associated with the crystal, for adjusting the potential across said crystal to cause the latter to function on a suitable portion of its current-potential characteristic.

13. A high frequency translating circuit including means for reducing the resistance thereof, said means comprising a second circuit coupled to said translating circuit the second circuit including a negative resistance rectifying crystal, and biasing means, electrically associated with the crystal, whereby the latter functions as a resistance compensating device.

14. In combination with the translating circuit, a second circuit containing a mineral rectifier, the mineral being one of a group having the property of acting as a negative resistance when subjected to a certain voltage, and a source of potential connected to the rectifier.

HENRY JOSEPH ROUND. NOEL MEYER RUST. 

